Isomerization of cyclop araffins of



p 0, 9- R. N. SHIRAS ET AL 23,151

ISOMERIZATION OF CYCLOPARAFFINS OF NONHYDROAROMATIC STRUCTURE OriginalFiled Oct. 18, 1946 Exfracf ve Dismlahon Column F'rac'h naTorD'us'fiNaTion olumn FracfionoTor v l r 6TH pperlnvenrors'. Russell Nsh'n-as Alan C.Nn on Cor-l H.D2al,Jn

EH fheir Aqent{%% Reissued Sept. 20, 1949 ISOMERIZATION OFCYCLOPABAFFINS OF NONHYDEQOAROMATIC STRUCTURE Russell N. Shire kland,Alan C- Nix n, B rkei y, signors to Francisco,

and Carl H. Deal, Jr., Alameda,

Shell Development Company, Calif, a corporation of Delaware Calif. as.-

San

Original No. 2,460,852, dated February 8, 1949,

Serial No. 703,992, October 18, tion for reissue July 16, 1949,

8 Claims.

This invention relates to the production of cycloparaflins ofhydroaromatic structure from hydrocarbon mixtures of relatively wideboiling range such as naphthenic gasolines or fractions thereofcomprising cycloparaffins of hydroaromatic structure and nonhydroaromatic structure in admixture with open chain paraffin andaromatic hydrocarbons. The invention relates more particularly to animproved process for the more efiicient production of cyclohexane fromnaphthcnic gasolines and fractions thereof comprising m thvlov op ntaneand ycl x n Realization of the full advantages inherent in processesrelying upon .cycloparaffins of hydro aromatic structure, such as, forexample, cyclohexane, as a starting or intermediate material is oftendependent upon efficient practical scale production of suchcycloparaflins from the available complex hydrocarbonmixtures comprisingthem. Not only is it imperative that they be produced with high yields,but it is essential that the product obtained be of a relatively highpurity and yet involve the use of a minimum of operative steps in theirproduction.

Sources of cyeloparaifins of hydroaromatic structure include theavailable hydrocarbon mixtures such as, for example, the naphthenic,natural and straight run gasolines, etc. Other sources includehydrocarbon mixtures of naphthenic character, boiling in the gasolineboiling range obtained by fractionation of the products of the processinvolving the thermal or catalytic treatment of hydrocarbons orcarbonaceous materials. Efficient production of a cycloparaffin ofhydroaromatic structure such as, for example, cyclohexane from suchreadily available hydrocarbon mixtures of naphthenic character involvesnot only the problem of recovering at least a substantial part of thecyclohexane inherently present in such mixtures, but the simultaneousconversion of the cycloparaffins of non-hydroaromatic structure tocycloparaflins of hydroa-romatic structure, such as the conversion ofthe initially present methylcyclopentane to cyclohexane. The readilyavailable naphthenic hydrocarbon mixtures as is well known, however,consist of highly complex mixtures of a plurality of individualhydrocarbons, many of which have similar or closely approximatingboiling temperatures, and many of which are capable of formingazeotropes with one another during the conditions of fractionaldistillation.

Separation of cycloparafiins free of any substantial amount ofimpurities from such complex mixtures by such methods of fractionalclistills- 1946. Applicae Serial No- 105.2%

(Cl. 26U6 6) tion disclosed heretofore, if at all possible, is oftenrendered so involved and delicate an opertion as to render it highlyimpractical. Resort to such expedients as the initial separation of afraction comprising both methylcyclopentane and cyclohexane, subjectionof this'fraction to cyclo arafiin isomerizin conditions, andtractionation. of the is meriza e by method disc in pro ess s heret f reis the efore unsatisfactory- Not o y do they enable the atta nment fonly relatively low conversiohsof cycloparaflins of nonhy rn t otructure to oyol p ra fi s f yroaronlatic s ru ure but th p o uc h r btaned w l generally ompris s b a l m ts of am ant mat rials su h as ar anshy rocarbons and open ch in p ra fin the ilin temperatures or whi h l oclose to os of the desired cyoloparafflns as to ender t ir s p ationther fr m by such exp di h as si ple fract ohatiQn by ethod d sc osed hr or impractical. In the production of cyclohexane f r dily availablenanhthen c hydro a n mixtures by such methods h crolopa afiins duce wi lbe c ntaminated w h substantial amounts of the benzene and.dimethylpen-tanes O inally present in the char e.- A se ious dif cul venerally inherent in p oc sses dis os heretofore wherein benzene isunavoidab a cumulated in the isomerizate is the hi hly d sadvantageouslimi ation upon th amount of unconverted material which can be recy l F0the removal of sufficient benzene to avoid an inordinate accumulation inthe system requires the rejection therewith of at least a substan ialpart of the unconverted material constituting the recycle stream in suchmethods, fiiince the suita y of a cyciohexan starting or intermediatematerial in many processes is dependen upon the absence therein to anysubstantialdegree of benzene and dimethyipcntanes, it is apparent thatthe practicability of a process producing cyclohexane from readilyavailable complex naphthenic hydrocarbon mixtures relies upon theability of the process to produce cyclohexane efiiciently an free of nysub tantial amount o henzene and dirnethyl-nentane. By the termhydroaromatic cycloparafiins, as used throughout the specification andappended cll t r s is meant the cycloparafiins having a hexamethylcneing such as, for examplalcyclohexane, and the allay-1 cyclohexanes, todistinguish them from oycloparaffins of non-hydroaromatic structure compisin th se having pentamethylene rings as, for example,methylcyclopentane and other cyclopentanes.

It is object at the present invention to proaisi vide an improvedprocess for the more efficient production of cycloparafiins ofhydroaromatic structure from hydrocarbon mixtures of relatively wideboiling range such as naphthenic gasolines, or fractions thereof,comprising cycloparaffins of hydroaromatic and non-hydroaromaticstructure in admixture with close boiling aromatic and open chainparaflinic hydrocarbons.

Another object of the invention is the provision of an improved processfor the more efiicient production of cyclohexane from hydrocarbonmixtures of relatively wide boiling range such as naphthenic gasolines.

A more particular object of the invention is the provision of animproved process for the more efficient production of cyclohexane of ahigh degree of purity from naphthenic gasoline fractions comprisingmethylcyclopentane, cyclohexane, benzene and close boiling open chainparaffinio hydrocarbons.

In accordance with the process of the invention a hydrocarbon mixture ofnaphthenic character such as for example a naphthenic straight rungasoline is subjected to fractionation to separate therefrom a fractionpredominating in hydrocarbons having the same number of carbon atoms tothe molecule and comprising cycloparaffins of non-hydroaromaticstructure and cycloparafiins of hydroaromatic structure in admixturewith close boiling aromatic and open chain paraflins. Thecycloparaflin-containing fraction thus obtained is subjected toextractive distillation conditions in the presence of a suitable solventas described more fully below to separate therefrom cycloparafiins of'hydroaromatic and L non-hydroaromatic structure free of any substantialamounts of close-boiling contaminants comprising open chain parafiinsand aromatic hydrocarbons. The cycloparaflins of non-hydroaromaticstructure free of any substantial amount of aromatic and open chainparafiins thus obtained are subjected to cycloparafiin isomerizingconditions converting cycloparafiins of non-hydroaromatic structure tocycloparaflins of hydroaromatic structure.

In a preferred embodiment of the invention the cycloparaflin-containingfraction separated from the naphthenic gasoline and includingcycloparaifins of hydroaromatic and non-hydroaromatic structure inadmixture with close boiling contaminants comprising open chainparaiiins and aromatic hydrocarbons, is subjected to an extractivedistillation in a'first extractive distillation zone. In the firstextractive distillation zone a raflinate fraction comprising parafiinichydrocarbons is separated from an extract fraction comprisingcycloparafiins of hydroaromatic and non-hydroaromatic structure inadmixture with aromatic hydrocarbons having the same number of carbonatoms to the molecule as the cycloparaflins. The extract fraction fromthe first extractive distillation zone is passed into a cycloparafiinseparating zone wherein a vapor fraction comprising cycloparafiins ofnon-hydroaromatic structure and aromatic hydrocarbons is separated froma liquid fraction comprising cycloparaflins of hydroaromatic structurefree of any substantial amount of aromatics. The vapor overhead from thecycloparaffin separating zone is passed into a second extractivedistillation zone. In the second extractive distillation zone arafiinate comprising cycloparaflins of non-hydroaromatic structure freeof any substantial amount of aromatics is separated from anextactfraction comprising aromatic hydrocarbons. The raflinatecomprising cycloparaflins of non-hydroaromatic structure free of anysubstantial amount of aromatics is introduced into a cycloparaflinconversion zone. In the conversion zone the cycloparaffins are subjectedto catalytic 'cycloparaifin isomerizing conditions effecting theconversion of cycloparaifins of non-hydroaromatic structure tocycloparaifins of hydroaromatic structure having the same number ofcarbon atoms to the molecule. Eflluence from the conversion zonecomprising cycloparafiins of hydroaromatic and nonhydroaromaticstructure is introduced into the cycloparaflin separating zone. As willbecome apparent from the following description thereof, the inventionenables not only the recovery of at least a substantial part of all ofthe cycloparafiin content of a cycloparaflin concentrate ascycloparafiins of hydroaromatic structure, but results in the obtainingof a product of a high degree of purity, devoid of even suchcontaminants as aromatics of close boiling range, with a minimum ofsteps and in the absence of many of the difficulties and complexitiesinherent in attempts to obtain a cycloparafiin product of a similardegree of purity by methods available heretofore.

In order to set forth more fully the nature of the invention, it will bedescribed in detail in its application to the production of cyclohexaneof a high degree of purity, free of any substantial amounts of benzene,from hydrocarbon mixtures of naphthenic character in the gasolineboiling range, with reference to the attached drawing in which thesingle figure represents a more or less diagrammatic elevational view ofa form of apparatus suitable for executing the process of the invention.

A hydrocarbon mixture of naphthenic character such as, for example, anaphthenic straight run gasoline, is forced from an outside sourcethrough valved line I by means of pump 2 into a feed fractionating zonecomprising fractionator 3. Within fractionator 3 a hexane fractioncomprising methylcyclopentane and cyclohexane is separated as anintermediate fraction. The methylcyclopentane cyclohexane fraction ispassed from fractionator 3 through line 4 into a second feedfractionator 5. Fractionation within fractionator 3 is preferablycontrolled to concentrate substantially all of the six carbon atomcycloparaiiins originally present in the feed in the intermediatemethylcyclopentane-cyclohexane fraction. Although the boiling range ofthe fraction thus obtained may vary within the scope of the invention,depending upon the particular origin of the composition of the feedmaterial, a hexane fraction boiling in the range of, for example, fromabout 65 C. to about C. has been found suitable. Within fractionator 5the hexane fraction is subjected to a second fractionation to effect theseparation of a higher boiling fraction as bottoms from a vapor overheadfraction comprising cyclohexane and methylcyclopentane. Operatingconditions within fractionator 5 may be controlled to include at least asubstantial part of the dimethylpentanes originally present in the feedin the liquid bottoms. Bottoms from fractionator 5 are withdrawntherefrom through valved line 6 and may be sent to additionalcycloparafiin separating means, not shown in the drawing, to efiect therecovery of any cyclohexane contained therein.

The vapor fraction is taken overhead from fractionator 5 and passedthrough valved line 8 into a first extractive distillation zone. Afraction comprising methylcyclopentane and cyclohexane from any suitableoutside source may be introduced into the system by means of valved lineH. Such a fraction may constitute a part of or all of thehydrocarboncharge to the system. The overhead fraction from tower'fraotionato-r 5 will comprise besides methylcyclopentane andcyclohexane a certain amount of open chain parafiins and at least asubstantial part of the benzene originally present the -charge.- Thefirst extractive distillation zone may comprise an extractivedistillation column [0. Within column ID the cyclopar'afli-nconcentrate'is subjected to an extractive distillation in the presenceof a suitable solvent introduced into the upper part of the column froma suitable source by means of line I3.

Solvents which may be employed in :column ll] include any solventmaterial enabling the separation of open chsiin paarraffins as a vaporfraction from a liquid traction comprising the solvent and thecycloparafiins :under extractive distillation conditions. Suitablesolvents comprise solvents for hydrocarbons which are higher boilingthan the cycloparaffins being distilled, are stable under the conditionsof distillation, do not react with any of the co1nponents of thehydrocarbon feed, and which markedly increase the volatility of. theopen chain parafiins relative to those of the cycloparafiins. Suitablesolvents comprise, for example, the polar liquids such as for exampleany of the polar solvents for .cycloparaflins higher boiling thancyclohexane having oxygen, nitrogen-', or sulfur-containing polar groupssuch as for example phenol, benzoic acid, isooutyric acid, aniline,N-methylaniline, :cyclohexylamine, acyclohexylaniline, dip'henylamine,:napthylamine, hexamethylamine diamine, benzaldehyde, furfuraldehyde,zenzoic anhydride, ethylbenzo'ate, benzophenone, acetophenone,cyclohe'xanone; benzoin, benzonitrile, nitrob'enzen'e, nitropropa-ne,pentachloroethane, diphenyl ether, acetal, acetamide, ethylphosphate,dimethylsulfolane, the alkyl-substituted suli olanes, etc. Thesolventemployed may consist of a single compound or of solutions of two or moreof such compounds or of aqueous solutions thereof.

Extractive distillation conditions withincolumn Ill are controlled toeffect the separation of .a vapor raffinate comprising open chainparaffins from a liquid extract comprising the solvent,methylcyclopentane and cyclohe-xane. The benzene present in the chargeto column ill will be included, under extractive distillation conditionsseparated as a vapor fraction *from a liquid fraction comprising thesolvent. Lean'solvent is returned from still Hi to the upper part ofcolumn In by means of valved line 13.

The process of the invention enables substantially complete recovery ofthe six carbon atom cycloparafiins originally present in the feed. In apreferred method of effecting such substantially complete'recovery ofall the six carbon atom cycloparaffins in thefeed. conditions infractiona tor 5 are controlled so that substantially all of thecyclohexane in the charge thereto is taken overhead. This will generallyresult in the inclusion of a proportion of the .dimethylpentanes in theoverhead. Dimethylpentanes thus included in the'overhead of fractionator.5 are separated therefrom to the degree desired in column 120 of thefirst extractive distillation zone. Inclusion of substantially all ofsuch .dimethylpentanes in the paraflinic overhead of column I 0 willoccasion the entrainment therewith of a certain amount of themethy'lcyclopentane. Whenimethylcyclo-penteen is thus included to asubstantial degree in the overhead from column .Irll it is perierablyrecovered therefrom by recycling at least -;a part of the overheadstream from line M throu h valved line 18 to line I leading intofractionator 3. The overhead from .column 1:!) (may be :passed, in part.or in its entirety, through valved line 29., to a separatefractionating zone represented in the drawing bythe single rractionator2 I. Within fractionator 2| a fraction comprising lighter boilingmaterials, such as open chain hexanes, is separated from a liquid higherboiling fraction comprising dimethylpentanes. Since the lower boiling ofthe six carbon atom cycloparaffins is readily separated by fractionationfrom dimethylpentane, an intermediate fraction comprisinmethylcyclopentane free of any substantial amount of dimethylpentane isseparated in fractionator 2i and removed therefrom by means of line 22.

Overhead from stripper lfi comprising methylcyclopentane, cyclohexaneand benzene, free of any substantial amount of dimethylpentanes, ispassed through line 24 into a cycloparaflin separating zone. Whenoperating the process with the passage of overhead from column It tofractionator 2|, the methylcyclopentane withdrawn from fractionator 2|through line 22, is passed in part or entirety into line 24 to combinetherein with'the cycloparafiin overhead from stripper It.

The cycloparaffin separating zone may com-- prise a fractionator 25. Infractionator 25 a fraction comprising cyclohexane is separated from avapor fraction comprising methylcyclo-- pentane and benzene. The liquidfraction comprising cyclohexane is withdrawn from fractionator 25 bymeans of valved line 26 and eliminated from the system as a finalproduct. The vapor fraction comprising methylcyclopentane and henacne iswithdrawn overhead from fractionator 25 and passed through valved line28 into a second extractive distillation zone. The second extractivedistillation zone may comprise an extractive distillation column 29.Within column 25 the hydrocarbon stream is distilled in the presence ofa suitable solvent which is introduced into the upper part of the columnby means of line '30. Extractive distillation conditions are controlledwithin column 39 to eifect the separation of a raffinate vapor overheadcomprising methylcyclopentane free of any substantial amount of benzenefrom a liquid extract fraction comprising solvent and benzene. Suitablesolvents for use in column 29 comprise those set forth for theseparation of cycloparaffins from open chain par-'- affins in columnIll. Thus good results are attained by the use of phenol or any otherpolar solvent for benzene which is higher boiling than benzene andstable under the operating conditions, to effect the indicatedseparation of methylcyclopentane from benzene.

The vapor fraction comprising methylcy-clopentane free of anysubstantial amount f henzene is passed from column 29 through line 35 toa conversion zone.

The liquid fraction comprising benzene and solvent is passed fromextractive distillation column 29 through line 3| into a stripper 32.Within stripper 32 benzene is stripped from the solvent and eliminatedas overhead therefrom through line 33. Lean solvent is withdrawn fromstripper l6 and passed through line 30 to column 29.

It is thus seen that the process of the invention enables not only thesubstantially complete recovery of cyclohexane free of any substantialamount of benzene from the charge, but provides for the separation of amethylcyclopentane charge for the conversion zone which is also free ofany substantial amount of benzene. Modification may obviously be madewithin the scope of the invention without departing from the spirit andscope thereof. Thus if desired the cycloparafiin-rich solvent withdrawnfrom column In may be stripped of only the methylcyclopentane instripper I6. Additional solvent may then be introduced from an outsidesource by means of valved line H. The substantially puremethylcyclopentane thus obtained overhead from stripper 16 may be passeddirectly to the conversion zone. To this effect a valved line 31 isprovided enabling the passage of hydrocarbons from line 24 into line 35leading to the conversion zone. When thus taking only methylcyclopentaneoverhead in stripper I6, the solvent now still containing cyclohexane aswell as benzene is drawn therefrom through line l3 and by-passed througha valved line 38 to suitable cyclohexane and benzene recovery means notshown in the drawing. Such recovery means may comprise one or moreseparate stripping zones as well as one or more separate solventextraction or extractive distillation zones. When the benzene is thusdiverted from the system through line 38 and no benzene is sent to thecycloparafiin separating column 25, the benzene-free overhead fromcolumn 25 may be passed directly to the conversion zone by means ofvalved lines 28, 34, 36 and 35.

When methylcyclopentane is passed from fractionator 21 through valvedline 22, such methylcyclopentane stream may also be introduced directlyinto the conversion zone. To this effect a valved line 39 is provided toenable the passage of methylcyclopentane from line 22 into line 35. Anoutstanding feature of the process of the invention is the efficientseparation of benzene from cyclohexane. The separation of benzene fromcyclohexane is greatly aided in column 25 by the presence therein ofsubstantial amounts of methylcyclopentane which is taken overhead withthe benzene. The passage of methylcyclopentane, even though free ofbenzene, from line 22, through line 24, into fractionator 25, may beresorted to to obtain the additional advantage of its presence upon theefficient separation of benzene from cyclohexane.

The conversion zone may comprise one or more reaction vessels such asfor example, a reactor 40, provided with suitable stirring means 4|.Within reactor 40 the methylcyclopentane is contacted with anisomerization catalyst under cycloparafiin isomerizing conditions.Suitable catalysts comprise those containing a metal halide of theFriedel-Crafts type, particularly those comprising a halide of aluminum,such as AlCla and/or AlBra. Particularly suitable catalysts comprise theorgano-aluminum halide complexes,

preferably a preformed aluminum chloride hydrocarbon complex. Othersuitable catalysts comprise those of the molten salt type containing thealuminum chloride in admixture with one or more halide-salts. Thetemperature in the conversion zone 40-is maintained in the range of fromabout 20 C. to about 150 C, and preferably from about 50 C. to about 95C. The specific temperature employed will be dependent to some extentupon the particular catalyst employed. When utilizing a preformedaluminum chloride hydrocarbon complex as the catalyst a temperature inthe range of from about 65 C. to about C. is somewhat preferred. Ahydrogen halide promoter, such as for example hydrogen chloride, ispreferably introduced into reactor 40 by means of line 42. The hydrogenchloride may be introduced inan amount of, for example, from about 0.1%to about 5% and preferably in an amount below about 1%. A greater orlesser amount of hydrogen halide may, however, be introduced into thereaction zone within the scope of the invention. Under these conditionsmethylcyclopentane is converted to cyclohexane within reactor 44.

Efliuence from reactor 40 comprising cyclohexane, and unconvertedmethylcyclohexane, entrained catalyst and hydrogen halide, is passedthrough line 43 into a catalyst separating zone, such as a separator 44.Within separator 44 a catalyst layer is separated from a supernatanthydrocarbon layer. Catalyst is passed from separator 44 through line 45to reactor 40. The hydrocarbon layer is passed from separator 44,through line 46, into an accumulator 41. Liquid comprisingcycloparaffins and dissolved hydrogen chloride is passed fromaccumulator 41 through line 48 into a stripping tower 49. Withinstripper 49 there is separated a vapor overhead comprising hydrogenhalide which is recycled through valved lines 5| and 42 to theconversion zone. A valved line 52 is provided for the introduction ofmakeup hydrogen chloride into the system.

A liquid fraction comprising cyclohexane and unconvertedmethylcyclopentane is taken from the lower part of stripper 45 andpassed through line 54 into fractionator 25. To aid in avoiding theaccumulation of light materials within the system without loss ofvaluable cycloparafiins, a part of the overhead from fractionator 25 maybe passed intermittently or continuously from line 28, through line 34,into line 8 leading to the first extractive distillation column I0.

A further signal advantage of the process of the invention resides inthe ability to employ a total recycle from the isomerization zonetherein. Due to the substantially complete elimination of benzene fromthe reactor charge without loss of any substantial amount ofcycloparafiins from the system, all of the methylcyclopentane content ofthe reactor effiuence isreturned to the reaction zone, thereby attainingsubstantially complete conversion to cyclohexane of allmethylcyclopentane charged to the process and its recovery as abenzene-free product. The invention therefore eliminates thedifficulties often inherent in processes disclosed heretofore, whereinat least a substantial portion of the cycloparaffin-containing recyclestream must be sacrificed to effect the elimination of sufficientbenzene to prevent its accumulation within the system.

The following example is illustrative of the practical scale productionof high purity, benzene-free cyclohex'ane from a naphthenic straight:run gasoline in accordance with the process ofthe invention:

Example.

In a continuous plant scale operation, 8.200 barrels. of straight: runnaphthenic gasoline containing 1.1% of methylcyclopentane, 2..2'3 of;cyclohexane. and 0.83% of benzene. by volume, are subjected to a. firstfractional distillation to separate therefrom a hexane. fraction boilingin the range offrom about 65 C. to about; 85 C. The resulting hexane.fraction is subjected to a. second fractionation to separate therefrom aC6 cycloparaflin concentrate; boiling: in the range. of from about 65 C.to. about '18. C1 containing 41.14% methylcyclopentane, 11.10%cyclohexane, 4.5% benzene and- 2..2;8% dimethylpentanes, the remainderof the concentrate consisting es.- sentially of lower boiling and higherboiling parafiins.

The C6 cycloparafli'n concentrate thus obtained is: subjected to afirst. extracted distillation in the presence of phenol as thev solventto separate an overhead raiiinate consisting essentially of paraflinsfrom a liquid bottoms extract consisting essentially of solvent,cycloparaffin and aromatics. The rich extract-containingsolvent isstripped to obtain an extract fraction consisting essentially ofmethylcyclopentane, cyclohexane and benzene, substantially free ofparafiins, which is passed into a cycloparafiin fractionator into whichthe hydrocarbon effluent from the subsequent reaction zone is alsointroduced. In the cycloparaflin fractionator a vapor overheadcontaining methy-lcyclopentane and aromatics is separated from a liquidbottoms fraction consisting essentially of benzene-free cyclohexane. Theoverhead from the cycloparafiin fractionator contains 7.5% normalhexane, 84.07% methylcyclopentane, 0.9% cyclohexane and 6.07% benzene.The overhead from the cycloparafiin fraciionator is subjected to asecond extractive distillation in the presence of phenol as the solventresulting in the obtaining of a substantially benzene-free raffinatecontaining 8% normal hexane, 89.4% methylcyclopentane and 1%cyclohexane. Benzene is stripped from the rich phenol solvent andrecovered as 99.8% pure benzene. The benzene-free raffinate from thesecond extractive distillation zone is subjected to cycloparaiiinisomerizing conditions by contact with an aluminum chloride-hydrocarboncomplex at a temperature of 80 C. and in the presence of a 0.4% H01. Thehydrocarbon components of the reactor efiiuent containing 40.7%methylcyclopentane and 48.7% of cyclohexane are passed directly into thecycloparafiin fractionator. 91.5% by volume content of cyclohexane isdrawn as the bottoms fraction from the cycloparaffin iractionator.Redistillation of this cyclohexane fraction results in a benzene-freecyclohexane of 95% purity. 87% of the combined mcthylcyclopentane andcyclohexane originally present in the gasoline charge to the system isthus recovered as benzene-free cyclohexane of 95% purity.

For the purpose of clarity, parts of apparatus such as pumps, coolers,reboilers, condensers, valves, etc, not essential to a completeunderstanding of the invention have been omitted from the drawing.Fractionating zones depicted in the drawin by single fractionators maycomprise the use of more than one iraetionator in.

Benzene-free liquid bottoms having a 10 the execution of the inventionon a practical scale. I a

The invention claimed is:

t. The process for the production of cyclohexane free of any substantialamount of benzene from naphthenic gasoline which comprises separatin-g afraction comprising methyl'cyclopentame and cyc-lohexane in admixturewith close boiling open chain paraifins and benzene from saidgasoline,subjectingsaid fraction to extractive distillation in a first extractivedistillat on zone, separating a raiiinate fraction comprising parafidnsfrom an extract fraction comprising methylcyclopentane, cycl'ohexane andbenzene in said first extractive distillation zone, passing said extractfraction from said first extractive distill'ation zone into acycloparaflin fractionating zone, separating a vapor fraction comprisingmethylcyclopentane and benzene from a liquid fraction comprisingcyclohexane free of any substantial amount of benzene in said cycloparahfin fractionating zone, passing said vapor trace tion from saidcycloparaflin fractionating zone into a second extractive distillationzone, separating a raifinate fraction comprising methyl-1 cyclopentanefree of any substantial amount of benzene from an extract fractioncomprising benzene in said second extractive. distillation zone,contacting said raflinate from said second extractive distillation zonewith an isomerization catalyst at: methylcyclopentane. isomerizingconditions in a. conversion zone, thereby converting mcthylcyclopentane.to cyclohexane in said conversion zone, passing eflluence from saidconversion zone into said cycloparaffin irac ien ne and withdrawing saidliquid fraction consisting essentially of .cyclohexane fre of anysubstantial amount. of benzene from aid y paraffin fraotionating zone.

2 The process for the. prod c on f. y eX- ane free of any substantialamount of benzene from nanhthenic gasoline which c mpr se parating afraction comprising methv-lcy 1cp n cane. and cycloh xane in admixturewith lose boiling open chain parafiins and benzene from said gasoline,subjecting sai fract on to ex tive distillation in a first extractive dstillation zone, separating a raflinate fraction comprising Daraffinsfrom an extract'iraction compri n methylcyclopentane, cyclohexane andbenz n in said first extractive distillation zone, passing sa d extractfraction from said first extractive distillation zone into. acycloparaiiin iractionating zone, separating a vapor fraction comprisingmethylcyclopentane and benzene from a liquid fraction comprisingcyclohexane free of any substantial amount of benzene in said.oycloparainn fractionating zone, passing said Vapor fraction from saidcycloparaflin fraotionatin zone into a second extractive distillationZon eparates a raffinate fraction comprising methylcyclopentane free ofany substantial amount of benzene from an extract fraction comprisingbenzene in said second extrac ive, disti ation on n ing said raflinatefrom said second extractive distillation z ne with an aluminum chlorideisomerization catalyst at methylcyclopentane isomerizing conditions in aconversion zone, thereby converting methylcyclopentane to cyclohexanesaid conversion zone, passing eiiluence from said conversion zone intosaid cycloparafiin fractionating zone, and withdrawing said liquidfraction consistin ess ntial y f yclchexane fr f any substantial amountof benzene from said cvclcparafiin i actiona ns zone 3. The process forthe production of cycloparaiiins of hydroaromatic structure free of any,substantial amount of aromatic hydrocarbons from a naphthenic gasolinewhich comprises separating a fraction comprising cycloparaffins ofhydroaromatic and non-hydroaromatic structure in admixture with closeboiling open chain parafiin and aromatic hydrocarbons from saidgasoline, subjecting said fraction to extractive distillation in a firstextractive distillation zone, separating a rafiinate fraction comprisingparafiins from an extract fraction comprising cycloparaffins ofhydroaromatic and non-hydroaromatic structure in admixture with closeboiling aromatic hydrocarbons in said first extractive distillationzone, passing said extract fraction from said first extractivedistillation zone into a cycloparaifin fractionating zone, separating avapor fraction comprising cycloparaflins of non-hydroaromatic structureand close boiling aromatic hydrocarbons from a liquid fractionconsisting essentially of cycloparafiins of hydroarom'atio structurefree of any substantial amount of aromatic hydrocarbons in saidcycloparafiin fractionatin zone, passing said vapor fraction from saidcycloparafiin fractionating zone into a second extractive distillationzone, separating a raffinate fraction comprising cycloparafilns ofnon-hydroaromatic structure free of any substantial amount of aromatichydrocarbons from an extract fraction comprising aromatic hydrocarbonsin said sec ond extractive distillation zone, contacting said raflinatefraction from said second extractive distillation zone with anisomerization catalyst at cycloparafiin isomerizing conditions in aconversion zone, thereby converting cycloparaifins of non-hydroaromaticstructure to cycloparafiins of hydroaromatic structure in saidconversion zone, passing eflluence from said conversion zone into saidcycloparaflin fractionating zone, and withdrawing said liquid fractionconsisting essentially of cycloparafiins of hydroaromatic structure freeof any substantial amount of aromatic hydrocarbons from saidcycloparaffin fractionating zone.

4. The process for the production of cyclohexane free of any substantialamount of benzene from a hydrocarbon fraction comprisingmethylcyclopentane and cyclohexane in admixture with close boiling openchain paraffins and benzene, which comprises subjecting said fraction toextractive distillation in a first extractive distillation zone,separating a rafiinate fraction comprisin parafiins from an extractfraction comprising methylcyclopentane, cyclohexane and henzene in saidfirst extractive distillation zone, passing said extract fraction fromsaid first extractive distillation zone into a cycloparafiinfractionating zone, separating a vapor fraction comprisingmethylcyclopentane and benzene from a liquid fraction comprisingcyclohexane free of any substantial amount ofbenzene in saidcycloparafiin fractionating zone, passing said vapor fraction from saidcycloparaflin fractionating zone into a second extractive distillationzone, separating a raflinate fraction comprising methylcyclopentane freeof any substantial amount of benzene from an extract fraction comprisingbenzene in said second extractive distillation zone, contacting saidraffinate from said second extractive distillation zone with anisomerization catalyst at methylcyclopentane isomerizing conditions in aconversion zone, thereby converting methylcyclopentane to cyclohexane insaid conversion zone, passing effluence from 12 said conversion zoneinto said cycloparamn fractionating zone, and withdrawing said liquidfraction consisting essentially of cyclohexane free of any substantialamount of benzene from said cycloparaffin fractionating' zone.

5. The process for the production of cyclohexane free of any substantialamount of benzene from a hydrocarbon fraction comprisingmethylcyclopentane and cyclohexane in admixture with close boiling openchain paraffins and benzene, which comprises subjecting said fraction toextractive distillation in a first extractive distillation zone,separating a raflinate fraction comprising parafiins from an extractfraction comprising methylcyclopentane, cyclohexane and benzene in saidfirst extractive distillation zone, passing said extract fraction fromsaid first extractive distillation zone into a cycloparaflinfractionating zone, separating a vapor fraction comprisingmethylcyclopentane and benzene from a liquid fraction comprisingcyclohexane free of any substantial amount of benzene in saidcycloparafiin fractionating zone, passing said vapor fraction from saidcycloparaflin fractionating zone into a second extractive distillationzone, separatin a raflinate fraction comprising methylcyclopentane freeof any substantial amount of benzene from an extract fraction comprisingbenzene in said second extractive distillation zone, contacting said,raflinate from said second extractive distillation zone with analuminum' halide isomerization catalyst at methylcyclopentaneisomerizing conditions in a conversion zone, thereby convertingmethylcyclopentane to cyclohexane in said conversion zone, passingefiluence from said conversion zone into said cycloparaffinfractionating zone, and withdrawing said liquid fraction consistingessentially of cyclohexane free of any substantial amount of benzenefrom said cycloparaflin fractionating zone.

6. The process for the production of cycloparaffins of hydroaromaticstructure free of any substantial amount of aromatic hydrocarbons from ahydrocarbon fraction comprising cycloparaffins of hydroaromatic andnon-hydroaromatic structure in admixture with close boiling open chainparafiin and aromatic hydrocarbons, which comprises subjecting saidfraction to extractive distillation in a first extractive distillationzone, separating a raffinate fraction comprising paraflins from anextract fraction comprising cycloparaffins of hydroarom'atic andnonhydroaromatic structure in admixture with close boiling aromatichydrocarbons in said first extractive distillation zone, passing saidextract fraction from said first extractive distillation zone into acycloparafiin fractionating zone,

separating a vapor fraction comprising cycloparafiins ofnon-hydroaromatic structure and close boiling aromatic hydrocarbons froma liquid fraction consisting essentially of cycloparafiins ofhydroaromatic structure free of any substantial amount of aromatichydrocarbons in said cycloparaffin fractionating zone, passing saidvapor fraction from said cycloparafiin fractionating zone into a secondextractive distillation zone, separating a raflinate fraction comprisingcycloparaffins of non-hydroaromatic structure free of any substantialamount of aromatic hydrocarbons from an extract fraction comprisingaromatic hydrocarbons in said second extractive distillation zone withan isomerization catalyst at cycloparafi'in isomerizing conditions in aconversion zone, thereby converting cycloparaffins of non-hydroaromaticstructure to cycloparaflins of hydroaromatic structure in saidconversion zone, passing eflluence from said conversion zone into saidcycloparaflin fractionating zone, and withdrawing said liquid fractionconsisting essentially of cycloparaffins of hydroaromatic structure freeof any substantial amount of aromatic hydrocarbons from saidcycloparafiin fractionating zone.

7. The process for the production of cyclohexane free of any substantialamount of benzene from a hydrocarbon fraction comprisingmethylcyclopentane and cyclohexane in admixture with close boiling openchain parafiins and benzene which comprises subjecting said fraction toextractive distillation in a first extractive distillation zone,separating a raffinate fraction comprising paraffins andmethylcyclopentane from an extract fraction comprisingmethylcyclopentane, cyclohexane and benzene in said first extractivedistillation zone, passing said raffinate fraction from said firstextractive distillation zone into a methylcyclopentane fractionatingzone, separating a fraction comprising methylcyclopentane from afraction comprising parafiins in said methylcyclopentane fractionatingzone, passing said extract fraction from said first extractivedistillation zone and said methylcyclopentane fraction from saidmethylcyclopentane fractionating zone into a cycloparaflin fractionatingzone, separating a vapor fraction comprising methylcyclopentane andbenzene from a liquid fraction comprising cyclohexane free of anysubstantial amount of benzene in said cycloparafiin fractionating zone,passing said vapor fraction from said cycloparaffin fractionating zoneinto a second extractive distillation zone, separating a rafi'matefraction comprising methylcyclopentane free of any substantial amount ofbenzene from an extract fraction comprising benzene in said secondextractive distillation zone, contacting said raffinate from said secondextractive distillation zone with an isomerization catalyst atmethylcyclopentane isomerizing conditions in a conversion zone, therebyconverting methylcyclopentane to cyclohexane in said conversion zone,passing efiluence from said conversion zone into said cycloparaffinfractionating zone, and Withdrawing said liquid fraction consistingessentially of cyclohexane free of any substantial amount of 14 benzenefrom said cycloparaflin fractionating zone.

8. The process for the production of cyclohexane free of any substantialamount of benzene from a hydrocarbon fraction comprisingmethylcyclopentane and cyclohexane in admixture with close boiling openchain paraifins and benzene which comprises subjecting said fraction toextractive distillation in a first extractive distillation zone,separating a raflinate fraction comprising parafiins andmethylcyclopentane from an extract fraction comprisingmethylcyclopentane, cyclohexane and benzene in said first extractivedistillation zone, passing said raifinate fraction from said firstextractive distillation zone into a methylcyclopentane fractionatingzone, separating a fraction comprising methylcyclopentane from afraction comprising paraflins in said methylcyclopentane fractionatingzone, passing said extract fraction from said first extractivedistillation zone into a cycloparafiin fractionating zone, separating avapor fraction comprising methylcyclopentane and benzene from a liquidfraction comprising cyclohexane free of any substantial amount ofbenzene in said cycloparaflin fractionating zone, passing said vaporfraction from said cycloparafiin fractionating zone into a secondextractive distillation zone, separating a rafiinate fraction comprisingmethylcyclopentane free of any substantial amount of benzene from anextract fraction comprising benzene in said second extractivedistillation zone, contacting said rafiinate from said second extractivedistillation zone and said methylcyclopentane fraction from saidmethylcyclopentane fractionating zone with an isomerization catalyst atmethylcyclopentane isomerizing conditions in a conversion zone, therebyconverting methylcyclopentane to cyclohexane in said conversion zone,passing effluence from said conversion zone into said cycloparaflinfractionating zone, and withdrawing said liquid fraction consistingessentially of cyclohexane free of any substantial amount of benzenefrom said cycloparaffin fractionating zone.

RUSSELL N. SHIRAS. ALAN C. NIXON. CARL H. DEAL, JR.

No references cited.

